Chemistry Reference
In-Depth Information
then fi nd its way into laboratories as tool for applications outlined in the next
section.
18.4
Applications
A key factor favoring the use of plant lectins in diverse assays is their stability.
Also, they can usually be labeled without harming their activities to detect car-
bohydrate-dependent binding to cells or tissue sections (for detailed protocols,
please see [9]). As summarized in Table 18.3, their glycan specifi city (for details,
please see Table 18.1) makes structural analysis and separation of mixtures of
glycans or glycoconjugates possible. Thus, disease-associated alterations of the
glycophenotype of cells become readily detectable (please see Chapter 25.2 for
examples and Chapter 14.4-6 for technical aspects of arrays). One of the most
frequent applications in immunology remains the stimulation of mitosis in lym-
phocytes, whose detection is recounted in Info Box 1. Mostly T cells are affected,
but in certain cases also B cells respond [10]. This cellular activity and also induc-
tion of mediator release such as proinfl ammatory cytokines have nourished the
assumption of a therapeutic potential for plant lectins, for example by stimulating
antitumor defense mechanisms. However, as it turned out, respective experi-
ments have not validated this assumption, even pointing to growth- stimulatory
effects not only on lymphocytes but also on tumor cells
in vitro
and
in vivo
[2,
11]. In general, these results also epitomize the effects of plant lectins on mam-
malian cells. This widely documented elicitor activity and the widespread occur-
rence of plant lectins let us expect a series of biological functions in plants.
18.5
Biological Functions
At the outset, the diversity of lectins both in structure and in carbohydrate specifi c-
ity makes it questionable that a common biological role can be attributed to all
lectins. In principle, the main concepts to answer the given question can be
grouped into two categories: to assume interaction of a lectin with exogenous
ligands or with binding partners in the plant. Table 18.4 is presented accordingly,
summarizing the evidence for lectin activities, starting with a defence function.
Toxic lectins such as those from castor (
Ricinus communis
) and French beans can
apparently protect the nutritious seeds from predators. If insuffi ciently cooked,
consumption of French beans can lead to severe gastrointestinal irritations.
However, a lectin/toxin will not necessarily be a biohazard to all animals. Fittingly,
the effects of plant lectins on insects are rather specifi c and can neither be
predicted nor generalized [11]. That legume seeds contain lectins in abundant
quantities and that legume roots are the site for symbiosis with nitrogen-
fi xing bacteria led to the idea that lectins may participate in initiating the plant-
